Page:Scientific Memoirs, Vol. 1 (1837).djvu/287

 Rh question, which is not only of itself of considerable importance, but the solution of which might also throw some light on the true mode of action possessed by these decolorizing compounds, the uses of which are daily multiplied in medicine and the arts.

I think that I have succeeded in proving that these compounds are really saline combinations of a peculiar acid formed of chlorine and oxygen. It is this acid, which I have isolated, that forms the subject of this essay, in which I shall treat successively of the manner of obtaining it, of the properties by which it is distinguished, the proofs of its composition, and the generic characters of the combinations which it forms.

Until a knowledge of the proportion of its elements, of which I shall treat in a following paragraph, allows of my stating the true name which the rules of chemical nomenclature assign to this acid, I shall continue to call it chlorous acid, and designate its compounds by the name of chlorites.

When reflecting on the best mode of proceeding in these researches, it will be soon perceived in reasoning on the hypothesis of the existence of chlorites, that the question would be on the point of being determined, if the supposed chlorite could be separated from the chloride with which it is considered as mixed in the decolorizing compound. Nothing would be easier to perform, if there existed a metal which would form with chlorine a compound soluble in water, and the oxide of which could at the same time form with the chlorous acid a compound insoluble in this liquid. But, unfortunately, all the known decolorizing compounds are soluble in water, and therefore nothing is to be hoped for in this respect.

This separation would also be very easy if, on the contrary, a metal was known which would form an insoluble compound with chlorine, and the oxide of which, by uniting with chlorous acid, would form a soluble and stable compound, up to a certain point. But the metallic chlorides are all soluble in water, except chloride of silver, lead, and protochloride of mercury; these three metals are therefore evidently those only which afford a choice.

Economical motives made me at first think of the salts of protoxide of mercury and of lead; but I soon found that no good result could be obtained by employing them.

When a solution of chloride of lime or of soda is treated with protonitrate of mercury, there is immediately precipitated a great quantity of protochloride of mercury, and the supernatant liquid is strongly decolorizing; but this property soon disappears, and the liquor then contains a notable quantity of deutochloride of mercury: the precipitate soon becomes red, and changes to an oxichloride.